Intramuscular injections are used to administer medication that requires a relatively quick uptake by the body with a reasonably prolonged action. With an intramuscular injection, the skin is punctured with a needle and the medication is administered deep into a large muscle of the body.
Intramuscular injections are either administered by a medical professional or are self-administered and can be administered using a pre-filled injection device or, first drawing the medication up through a needle into an injection device from a separate vial and then administering the medication. As far as ease of use, it is preferable to use a pre-filled injection device since there is no need to draw up medication from a separate vial into the injection device. Moreover, in some cases when medication needs to be drawn up into the injection device from a separate vial, the needle of the injection device needs to be changed after the medication has been drawn up into the injection device. Many protocols recommend using a filtered needle or a small needle to draw up medication from a vial to an injection device in order to reduce any likelihood that glass or other debris will be injected into the patient and then, preferably, changing the needle, switching to a larger needle appropriately sized for the size of the patient and the specific injection site. Both of these draw backs, transferring medication from a separate vial to an injection device and changing needles are avoided when a pre-filled injection device is used (Cocoman A. & Murray J. (2008) Journal of Psychiatric and Mental Health Nursing 15, 424-434).
However, most pre-filled injection devices, specifically automatic ones are complex and expensive to manufacture and in some cases, are not capable of delivering medication at a slow, steady rate, preferably not to exceed 1 mL per 10 seconds. A slow, steady rate promotes comfort and allows time for the tissues to expand and begin absorbing the solution. Examples of injection devices are described in EP2623143, US20050124940, U.S. Pat. No. 8,262,604 and US20080195056.